Modular construction of a liquid hydrogen storage tank with a common-access tube and method of assembling same

ABSTRACT

A storage tank having an inner vessel disposed within an outer vessel. A common-access tube or conduit is used to route the various fluid flow lines into the interior of the inner vessel. The common-access tube facilitates modular construction and assembly of the storage tank.

FIELD OF THE INVENTION

The present invention relates to storage tanks, and more particularly toliquid hydrogen storage tanks.

BACKGROUND OF THE INVENTION

Typical multi-layered vacuum super insulated cryogenic tanks utilize apair of cylindrical inner and outer tanks that are arrangedconcentrically with the inner tank residing in an interior of the outertank. There are multiple radiant heat shields (insulation layers),approximately 30-80, coiled around the inner tank between the inner andouter tanks. A high vacuum exists between the inner and outer tanks tofurther prevent heat transfer. This type of thermal insulation is calleda multi-layered vacuum super insulation. These storage tanks are capableof storing fluids at cryogenic temperatures.

The inner tank is positioned within the outer tank so that the innertank does not contact, the outer tank and so that thermal conductionpaths between the inner and outer tanks are minimized. The fluid issupplied to and removed from the inner tank through a plurality ofdiscrete fluid lines that extend through the outer tank, the vacuumbetween the inner and outer tanks, and into the inner tank at separatelocations. Each of these fluid lines is a conductive heat path that canresult in parasitic heat leaks into the inner tank.

The fluid lines are typically of a double wall construction inside theinner tank with a vacuum insulation therebetween to reduce the parasiticheat leaks into the inner tank. The double wall vacuum insulation sharesthe vacuum with the gap between the inner and outer tanks. Thisconstruction has various drawbacks. The use of discrete double wallfluid lines is labor intensive and makes automated production difficult.Additionally, the use of discrete double wall fluid lines results inmultiple obstructions in the wrapping of the insulation layers aroundthe exterior of the inner tank. The insulation layers need to be cut foreach of these obstructions. Each of these cuts/breaks in the insulationlayers results in a potential thermal shortcut for a parasitic heat leakinto the inner tank. Furthermore, the cutting of the insulation layersis time consuming and makes automated production difficult. Thus, itwould be advantageous to provide a storage tank that reduces orminimizes these drawbacks.

SUMMARY OF THE INVENTION

The present invention reduces and/or eliminates one or more of theabove-described drawbacks. The present invention utilizes acommon-access tube or conduit to route the various fluid lines into theinterior of the inner tank. The common-access tube shares the vacuumbetween the inner and outer tanks. The use of a single common-accesstube facilitates modular construction and assembly of the storage tank.

In one aspect of the present invention, a cryogenic storage tank isdisclosed. The tank includes a fluid-tight outer vessel and afluid-tight inner vessel disposed within the outer vessel. There is avacuum between the inner and outer vessels. A tube communicates with thevacuum and extends into an interior of the inner vessel. A first portionof the tube within the interior of the inner vessel has a firstcross-sectional area of a first value. A second portion of the tubewithin the interior of the second vessel has a second cross-sectionalarea of a second value which is greater than the first value. The secondportion is an end portion of the tube. There is a plurality of fluidlines extending from an exterior of the inner vessel to an interior ofthe inner vessel through the tube.

In another aspect of the present invention, a modular component for acryogenic storage tank is disclosed. The modular component includes atube having first and second ends and an end plate on the second end ofthe tube. There is a plurality of fluid flow lines extending through thetube and through the end plate with a fluid-tight connection between anexterior of the fluid supply lines and the end plate. The tube, endplate and fluid flow lines are connected together as a single assemblyoperable to be attached to an inner vessel of a cryogenic storage tankprior to the inner vessel being enclosed within an outer vessel of thecryogenic storage tank.

In yet another aspect of the present invention, a method of assembling acryogenic storage tank having a fluid-tight inner vessel located withina fluid-tight outer vessel and a plurality of fluid flow lines extendingfrom an exterior of the outer vessel to an interior of the inner vesselthrough a common-access tube is disclosed. The method includes: (1)attaching a plurality of fluid flow lines to an end plate with firstportions of the fluid flow lines extending beyond a first side of theend plate and second portions of the fluid flow lines extending beyond asecond side of the end plate, the end plate configured to be disposed inthe common-access tube with the first side of the end plate exposed tothe interior of the inner vessel and the second portions of the fluidflow lines within the common-access tube; and (2) attaching interiorfluid piping members a to the first portions of the fluid flow lines.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a fragmented front plan view of a cryogenic storage tankaccording to the principles of the present invention with the end capsin phantom;

FIG. 2 is an end plan view of one end of the storage tank of FIG. 1;

FIG. 3 is an end plan view of the opposite end of the storage tank ofFIG. 1 showing the preloading mechanism;

FIG. 4 is a partial cross-sectional view within circle 4 of FIG. 1showing the overlap of the annular stiffening member with the centraland end segments of the outer tank;

FIGS. 5 and 6 are perspective views of the preloading mechanism used onthe storage tank of FIG. 1 with the preloading mechanism partiallycutaway in FIG. 6;

FIG. 7A is a partially cutaway front plan view of the storage tank ofFIG. 1 showing the common-access tube with flared end and the fluid flowlines passing therethrough;

FIG. 7B is an end plan view along line 7B-7B of FIG. 7A showing theattachment of the pipes within the common-access tube to the end plateon the flared end of the common-access tube;

FIG. 7C is a schematic representation of an alternate arrangement of acommon-access tube according to the principles of the present invention;

FIG. 8 is a perspective view of the corrugated piping used in thestorage tank of FIG. 1;

FIG. 9 is an end plan view of the tank of FIG. 1 showing the fluidpiping that passes into the central tube;

FIGS. 10A and 10B are simplified representations of the corrugationsthat can be utilized for the piping used in the storage tank of FIG. 1;

FIG. 11 is an end plan view of the storage tank of FIG. 1 showing theaddition of three sectional stiffening members;

FIG. 12 is a perspective view of one of the sectional stiffening membersof FIG. 11;

FIGS. 13A-F are cross-sectional views of various configurations for theannular stiffening members used in the storage tank of FIG. 1; and

FIGS. 14-17 are flowcharts of the various assembly steps for forming thestorage tank of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

A cryogenic storage tank 20 according to the principles of the presentinvention is shown in FIG. 1. Storage tank 20 includes an innertank/vessel 22 that is suspended within an outer tank/vessel 24 in aspaced relation therefrom. Inner and outer vessels 22, 24 are bothfluid-tight vessels. Inner vessel 22 is operable to store a fluid, suchas liquid hydrogen, therein at cryogenic temperatures. A plurality offluid flow lines 26 provide fluid flow paths from an exterior of outervessel 24 into an interior of inner vessel 22 and enter inner vessel 22through a common-access tube 28 (FIG. 7A), as described in more detailbelow. Fluid flow lines 26 allow a fluid to be inserted into and removedfrom the interior of inner vessel 22. A plurality of insulation layers30 are wrapped around the exterior of inner vessel 22 in the spacebetween the inner and outer vessels 22, 24. A vacuum exists betweeninner and outer vessels 22, 24 and within common-access tube 28. Theinsulation layers 30 and the vacuum reduce heat influx into the interiorof inner vessel 22. Storage tank 20 can be used on mobile platforms,such as vehicles, or in stationary applications.

Referring now to FIGS. 1, 2, 3 and 7A, inner vessel 22 includes acentral segment 40 and a pair offend segments or end caps 42, 44. Endcaps 42, 44 are welded to central segment 40 to define an interior spaceor volume 46 of inner vessel 22. Common-access tube 28 is attached, suchas by welding, to an opening in end cap 42 and extends from end cap 42into interior 46 of inner vessel 22. Common-access tube 28 is attachedto end cap 42 prior to end cap 42 being welded to central segment 40.Additionally, fluid flow lines 26 are also positioned through andsecured within common-access tube 28 prior to end cap 42 being welded tocentral segment 40, as described below. A bracket 48 is attached, suchas by welding, to an exterior of end cap 42. A tensioning mechanism 50is attached to end cap 44. Bracket 48 and tensioning mechanism 50provide attachment points for suspending inner vessel 22 within outervessel 24, as described below.

Outer vessel 24 includes a central segment 60 and two end segments orend caps 62, 64 that are welded to opposing ends of central segment 60.Central segment 60 has a generally uniform wall thickness. A pair ofannular stiffening members/rings 68 is welded to opposing end portions70 of central segment 60. Stiffening members 68 extend across thejuncture of central segment 60 with end caps 62, 64, as shown in FIGS. 1and 4. Stiffening members 68 provide support for central segment 60 andlimit deformation thereof due to the suspending of inner vessel 22within outer vessel 24, as described below. Stiffening members 68, dueto the overlapping of the juncture of central segment 60 with end caps62, 64, also serve to prevent sparks and other welding debris and gasesfrom entering into the space between inner and outer vessels 22, 24 andfrom contacting insulation layers, 30 therein when welding end cap 62,64 to central segment 60. Optionally, stiffening members 68 can beattached to the exterior of central segment 60, although all thebenefits of the present invention, may not be realized. The attachmentof end caps 62, 64 to central segment 60 provides additional support forcentral segment 60 and limits deformation thereof due to the suspendingof inner, vessel 22 within outer vessel 24.

Referring now to FIGS. 1-3, 5 and 6, details of the suspending ofinner-vessel 22 within outer vessel 24 are shown. Inner vessel 22 issuspended within outer vessel 24 with a plurality of suspension members80. A first group 82 of suspension members 80 is coupled to one endportion 70 of central segment 60 of outer vessel 24 and to end cap 42 ofinner vessel 22. A second group 84 of suspension members 80 is coupledto the other end portion 70 of central segment 60 of outer vessel 24 andto end cap 44 of inner vessel 22.

Each group 82, 84 includes three suspension-members 80 that are equallyspaced about each end cap 42, 44 of inner vessel 22. For example, eachsuspension member 80 is spaced apart about 120 degrees. Each suspensionmember 80 is a continuous cord in the form of a fixed-length loop.Preferably, each cord is flat and has a small cross-sectional area tominimize the heat path. The suspension members or cords can be made froma variety of materials. For example, each suspension member can be acarbon-fiber rope with an epoxy matrix. Such a material is stiff andreadily facilitates the manufacturing of such a cord in a closedcontinuous loop. Other materials include, but are not limited to, theuse of woven glass fiber, woven Kevlar fiber, and other rope-likematerials. It should be appreciated that while suspension members 80 arepreferably in the form of closed-loop cords, individual strips orsections of cords that are not looped can also be utilized. Such cordswould be secured to the appropriate attachment mechanisms coupled to thecentral segment 60 of outer vessel 24 hand to end caps 42, 44 of innervessel 22. It should also be appreciated that while three suspensionmembers 80 are shown as being used to support each end of inner vessel22, a single continuous suspension member (not shown) could be utilizedto support each end of inner vessel 22 by routing or wrapping eachsuspension member through the various attachment mechanisms associatedwith each side of storage tank 20 and providing three distinct tensilesegments that extend between each end of inner vessel 22 and outervessel 24.

In the embodiment shown, three suspension members 80 in the form ofclosed loops are used to support each end of inner vessel 22 withinouter vessel 24. Specifically, each suspension member 80 of first andsecond groups 82, 84 is wrapped around an associated roller 88 which iscoupled to one of the stiffening members 68 on each end portion 70 ofcentral segment 60 of outer vessel 24 by an associated bracket 90 andbolt 92. Each suspension member 80 of first group 82 is also wrappedaround an associated roller 94 coupled via a bolt 96 to bracket 48attached to the axial center portion of end cap 42 of inner vessel 22.Alternately, a portion of common-access tube 28 could extend (not shown)outwardly beyond end cap 42 and provide an attachment point for rollers94 in lieu of bracket 48. Each suspension member 80 of second group 84is also wrapped around an associated roller 100 which is coupled totensioning mechanism 50 attached to end cap 44 of inner vessel 22.Preferably, bracket 48 and tensioning mechanism 50 are attached toaxially center portions of each end cap 42, 44 of inner vessel 22 toprovide centralized support of inner vessel 22 within outer vessel 24.

Referring now to FIGS. 3 and 5-6, details of tensioning mechanism 50 areshown. A base plate 110 is attached to end cap 44 of inner vessel 22,such as by welding. A movable plate 112 is axially movable relative tobase plate 110 along fixed guides 114. Bracket members 115 are fixedlyattached to movable plate 112. Rollers 100 are bolted to bracket members115. A threaded adjusting member 116 extends through a threaded openingin movable plate 112 and contacts base plate 110. The threadedengagement between adjusting member, 116 and movable plate 112translates rotation of adjusting member 116 into axial movement ofmovable plate 112 relative to base plate 110 along guides 114. Asmovable plate 112 moves relative to base plate 110, the tension insuspension members 80 will vary.

To suspend inner vessel 22 within outer vessel 24, an inner vesselassembly is positioned within central segment 60 of outer vessel 24. Theinner, vessel assembly includes inner vessel 22 with insulation layers30 wrapped thereon and fluid flow lines 26 extending outwardly fromcommon-access tube 28. The portions of fluid flow lines 26 that areexterior to inner vessel 22 can be configured into a desired shape ororientation prior to the positioning of the inner vessel assembly withincentral segment 60. Alternately, the fluid flow lines 26 can remainstraight or out of way and be bent into a desired configuration aftersuspending inner vessel 22 within outer vessel 24. The suspension of theinner vessel assembly within outer vessel 24 is described in more detailbelow.

In the present invention, suspension members 80 are intended to be undertensile loading at all times. While suspension members 80 may have astiffness associated with their specific materials of construction, itshould be appreciated that suspension members 80 are not intended to besubjected to any appreciable compressive loading. Suspension members 80are sized to provide the required support of inner vessel 22 withinouter vessel 24 and for the fluids to be stored within inner vessel 22.Additionally, suspension members 80 are designed to be operable towithstand sudden accelerations/decelerations when storage tank 20 islocated on a movable platform, such as a vehicle. Furthermore, thedimensions of suspension members 80 are designed to minimize the heatpath into inner vessel 22. Moreover, it should be appreciated that theangle α at which suspension members 80 extend from their associatedbrackets on inner vessel 22 toward end portions 70 of central segment 60of outer vessel 24 relative to the axial axis of inner vessel 22provides differing amounts of axial support. The smaller the angle, thegreater the amount of axial support provided to inner vessel 22. On theother hand, the smaller the angle, the greater the intrusion ofsuspension members 80 into the interior space between inner and outervessels 22, 24. The larger intrusion decreases the volume of storagetank 20 for a given size tank. Thus, the angle α is chosen based on oneor more of these design considerations.

Stiffening members 68 serve to reinforce central segment 60 of outervessel 24 and limit the deformation of central segment 60 due to thesuspension of inner vessel 22 within outer vessel 24. Limiting thedeformation facilitates the aligning and attachment of end caps 62, 64to central segment 60. To accomplish this, brackets 90 are attached,such as by welding, directly to stiffening members 68 so that suspensionmembers 80 directly impart their tensile loading on stiffening members68. The tensile load on stiffening members 68 is transmitted to centralsegment 60 and distributed along end portions 70. Stiffening members 68can take a variety of cross-sectional shapes. For example, as shown inFIGS. 13A. and 13B, stiffening members 68 can be rectangular incross-section with the longer side extending either axially or radially,respectively. The cross-section of stiffening member 68 can be L-shaped,as shown in FIG. 13C, T-shaped, as shown in FIG. 13D, I-shaped, as shownin FIG. 13E, and inverted U-shaped, as shown in FIG. 13F. Each of thesedifferent cross-sectional configurations will provide support forsuspending inner vessel 22 within outer vessel 24 and limit thedeformation of outer vessel 24. It should be appreciated that thecross-sectional shapes shown for stiffening members 68 are merelyexemplary and that other cross-sectional shapes or combinations thereofcan be utilized. The particular cross-sectional shape chosen will varydepending upon the design needs of the particular storage tank 20 beingbuilt.

Referring now to FIGS. 11 and 12, an alternate configuration for thestiffening of outer vessel 24 is shown. In this configuration, threesectional stiffeners 120 are utilized on each end portion 70 of centralsegment 60 of outer vessel 24. Sectional stiffeners 120 are disposedbetween the attachment points for suspension members 80. Sectionalstiffeners 120 serve to provide additional, stiffening to the endportions 70 between suspension members 80. Sectional stiffeners 120 arepartially circular shaped in plan view and have a side edge 122 shapedto correspond to the interior of annular stiffening members 68.Sectional stiffeners 120 are welded to stiffening members 68 to provideadditional support thereto. It may be possible to use sectionalstiffeners 120 in lieu of annular stiffening members 68. That is,depending upon the design of central segment 60 and the loading impartedon central segment 60 by suspension members 80, the use of sectionalstiffeners 120 welded directly to end portions 70 may sufficiently limitdeformation of central segment 60 such that attachment of end caps 62,64 is not impeded. Thus, central segment 60 of outer vessel 24 can bereinforced with annular stiffening members 68, sectional stiffeners 120or a combination of both. These stiffening features of the presentinvention provide localized support for specific portions of centralsegment 60 of outer vessel 24 during assembly. These stiffening featuresalso provide localized support to both central segment 60 and end cap,62, 64 during operation of storage, tank 20. Additionally, it should beappreciated that the addition of end caps 62, 64 to central segment 60will also provide additional support for central segment 60 and supporta portion of the load imparted by the suspension of inner vessel 22therein. The use of such stiffening members advantageously provides thelocalized support and rigidity where, necessary without increasing thewall thickness or structural rigidity of central segment 60 solely toallow the suspension of inner vessel 22 therein prior to the attachmentof end caps 62, 64. Thus, the use of stiffening members enables the useof a central segment 60 having a thickness that is substantially uniformthroughout its axial length.

Referring now to FIGS. 7A and B, details of common-access tube 28 andthe routing of fluid flow lines 26 into the interior 46 of inner vessel22 are shown. A first end 140 of common-access tube 28 is attached toend cap 42 of inner vessel 22. A second end 142 of common-access tube 28is cantilevered into interior 46 of inner vessel 22. Common-access tube28 has an axial length between first and second ends 140, 142.Common-access tube 28 has a first portion 144 with a substantiallyuniform diameter and a second (flared) portion 146 having a changingdiameter. First and second portions 144, 146 share a common axial axis.An end plate 148 is welded to second end 142 of common-access tube 28and forms a fluid-tight seal therewith, as shown in FIG. 7B andindicated as W. A perforated end plate 150 (shown in FIG. 2) is disposedin first end 140. Fluid flow lines 26 run through common-access tube 28and into interior 46 of inner vessel 22 through end plates 148, 150.Preferably, as shown, all fluid flow lines 26 enter interior 46 of innervessel 22 through common-access tube 28. Additionally, it is alsopreferred that all communication/data/power/etc. lines, such as wires,connectors and cables, such as those connecting to a level sensor 152,are also routed through common-access tube 28 within one or more of thefluid flow lines 26. Level sensor 152 is attached to an exterior ofcommon-access tube 28 and is within interior volume 46 of inner vessel22. Level sensor 152 is operable to provide a signal indicative of theliquid level within inner vessel 22. The communication line 153 forlevel sensor 152 exits inner vessel 22 through one of the fluid flowlines 26. The use of common-access tube 28 to route all the piping andcommunication/data/power/etc. lines into interior 46 of inner vessel 22advantageously reduces the number of obstructions on the exterior ofinner vessel 22 around which insulation layers 30 must be routed.Additionally, the number of, heat flow shortcuts are reduced along withfacilitating the automated application of insulation layers 30.

First end 140 is preferably attached to an axial center portion of endcap 42 of inner vessel 22. This attachment location centralizes theobstruction caused by fluid flow lines 26 leaving inner vessel 22 andaligns with the bracket 48 used to attach first group 82 of suspensionmembers 80 to end cap 42 of inner vessel 22. The centralized aligning ofthese various features facilitates the wrapping of the insulation layers30, either manually or automated, which are generally wrapped in atangential direction and folded over on the end caps 42, 44.

Fluid flow lines 26 are spaced apart from the interior wall 154 ofcommon-access tube 28. Fluid flow lines 26 may touch one another or bespaced apart from one another within common-access tube 28. Preferably,fluid flow lines, 26 are spaced apart from one another. Fluid flow lines26 diverge from one another in flared portion 146 to pass through endplate 148 in a spaced relation, as shown in FIG. 7B. Preferably, fluidflow lines 26 are evenly spaced apart when passing through end plate148. The spacing facilitates the fluid-tight welding of each fluid flowline 26 to end plate 148. That is, the increased diameter of secondportion 146 allows fluid flow lines 26 to be spaced apart a distancesufficient to manipulate a welding device around the perimeter of eachfluid flow line 26 with limited interference caused by the adjacentfluid flow lines.

The volume of interior 46 of inner vessel 22 occupied by common-accesstube 28 is advantageously reduced with first portion 144 ofcommon-access tube 28 having a smaller diameter than flared portion 146.That is, if the entire length of common-access tube 28 were of adiameter sufficient to facilitate the welding of fluid flow lines 26 toend plate 148 with limited interference from each other, the overallvolume of common-access tube 28 within interior 46 of inner vessel 22would be increased. Increasing the volume of common-access tube 28decreases the fluid-holding capacity of inner vessel 22.

Common-access tube 28 is angled such that second end 142 is nominallylower than first end 140. This angling provides an advantageoustemperature profile along the fluid flow lines 26 and common-access tube28 wherein the colder fluid is at the lower elevation than the warmerfluid. This helps minimize parasitic heat leaks from natural convectioninside fluid flow lines 26. Preferably, common-access tube 28 extendssubstantially the entire axial length of inner vessel 22. By havingcommon-access tube 28 extending as far as possible within inner vessel22, a maximization of the heat-resisting effective length can berealized. It should be appreciated, however, that the total length thatcommon-access tube 28 can extend within interior 46 of inner vessel 22will be limited by the necessity of fluid flow lines 26 exiting endplate 148 and the space required to route fluid flow lines 26 to theirappropriate locations within interior 46 of inner vessel 22.

Referring now to FIG. 7C, a schematic representation of an alternateconfiguration for common-access tube 28′ is shown. In thisconfiguration, common-access tube 28′ has a substantially uniformdiameter and extends from a non-central portion of end cap 42′ of innervessel 22′. This configuration advantageously routes all the fluid flowlines 26′ into interior volume 46′ of inner vessel 22′ through a singleaccess location thereby minimizing the obstructions on the exterior ofinner vessel 22′ that must be accommodated by the insulation layers 30′.The uniform diameter of common-access tube 28′, however, encompasses agreater volume of inner vessel 22′ than that of common-access tube 28described above and shown in FIG. 7A.

Accordingly, the use of a common-access tube advantageously minimizesthe interference with applying insulation layers 30 to inner vessel 22.Additionally, use of a common-access tube also facilitates modularconstruction of cryogenic storage tank 20, as described in more detailbelow. Moreover, the use of a common-access tube can advantageouslyprovide a desired temperature profile and reduce heat paths into theinner vessel.

Referring now to FIGS. 7A, 8 and 9, details of fluid flow lines 26 areshown. Fluid flow lines 26 extend from the exterior of cryogenic storagetank 20 and outer vessel 24 into interior 46 of inner vessel 22. Fluidflow lines 26 pass through openings in outer vessel 24, through thespace between inner and outer vessels 22, 24 and into interior 46 ofinner vessel 22 through common-access tube 28. Fluid flow lines 26include a variety of different flow lines that each performs a differentpurpose or function. A liquid fill line 160 is used to fill inner vessel22 with the desired fluid, such as hydrogen, in liquid form. A gasextraction line 162 is used to extract the fluid from inner vessel 22 ina gaseous form. As such, the end of gas extraction line 162 withininterior 46 of inner vessel 22 is adjacent the uppermost portion ofcentral segment 40. A heat exchange loop 164 can be used to facilitatethe extraction of the fluid in gaseous form from inner vessel 22. Heatexchange loop 164 is used, to selectively route a heating fluid throughinterior 46 of inner vessel 22. The routing of the heating fluidincreases the temperature within inner vessel 22, thereby increasing thegaseous portion of the fluid stored therein. Additionally, the use ofheat exchange loop 164 can also facilitate the maintaining of a desiredoperational pressure within inner vessel 22, thereby also facilitatingthe extraction of the fluid therefrom. In place of heat exchange loop164, a liquid extraction line (not shown) could be employed. The liquidextraction line would have an end terminating in the lower portion ofcentral segment 40 of inner vessel 22 and be used to extract liquid frominner vessel 22. If desired, an external heater can be used to convertthe extracted liquid into gaseous form when it is desired to provide thefluid in gaseous form to a downstream component, such as a fuel cellstack or internal combustion engine.

Each fluid flow line 26 can be comprised of a plurality of discrete,unitary and uninterrupted sections or segments that are attachedtogether, such as by welding, to form the entire fluid flow line. Forexample, as shown in FIG. 7A, each fluid flow line 160, 162, 164 caninclude respective interior segments 160 a, 162 a, 164 a that are withininterior 46 of inner vessel 22. Middle segments 160 b, 162 b, 164 bextend from their respective interior segments through common-accesstube 28 and into the space between inner and outer vessels 22, 24.Exterior segments 160 c, 162 c, 164 c (shown in FIGS. 8 and 9) extendfrom the middle segments through the space between inner and outervessels 22, 24 and either extend to the exterior of storage tank 20 orconnect to other fluid piping lines attached to outer vessel 24 thatcommunicate with piping external to cryogenic storage tank 20.Alternately, each segment a, b, c can be combined into a large singleunitary uninterrupted segment that includes the interior, middle andexterior segments. As used herein, the term “unitary uninterrupted”segment or fluid flow line means that that segment or fluid flow line isformed in a continuous manner and not by the attaching of discretesegments to one another.

The portions of fluid flow lines 26 between inner and outer vessels 22,24 extend upwardly upon exiting common-access tube 28, as shown in FIG.9, to avoid a siphoning effect and to provide an advantageous thermalprofile. Additionally, gas extraction line 162, or a liquid extractionline, if so equipped, can be wrapped around the exterior of inner vessel22 in the space between inner and outer vessels 22, 24 to help with themaintaining of the low temperature in inner vessel 22 during theextraction of the fluid from inner vessel 22.

To facilitate the bending of the various fluid flow lines 26 into theirdesired orientation/configuration, each fluid flow line segment caninclude both corrugated portions and non-corrugated portions. Forexample, one segment of piping, such as that shown in FIG. 10A, caninclude multiple corrugated portions 170 with non-corrugated portions172 therebetween. Additionally and/or alternately, as shown in FIG. 10B,a different segment of fluid flow line can include multiplenon-corrugated portions 172 disposed around a corrugated portion 170.The number and location of corrugated portions 170 and non-corrugatedportions 172 will vary depending upon the desired orientation of theparticular fluid line segment when storage tank 20 is fully assembled.The corrugated portions can have varying gaps, heights land widths, ascan be seen by comparing the corrugated portions 170 in FIG. 10A withthe corrugated portions 170 in FIG. 10B. Additionally, the wallthickness of the particular fluid flow line can also vary. These variouscharacteristics of corrugated portions 170 affect its stiffness and howeasily it can be bent into a desired orientation. These characteristicsalso affect the maximum bend angle that can be imparted on thatparticular corrugated portion 170. Thus, not only will the numbering andarrangement of corrugated and non-corrugated portions 170, 172 vary forparticular segments of fluid flow lines, the type of corrugation (gap,height, width and wall thickness) can also vary to provide a fluid flowline segment that can be readily and easily bent into a desiredorientation for assembly of storage tank 20.

The various corrugated and non-corrugated portions 170, 172 of eachfluid flow line segment are made to correspond to the specific needs ofthe particular fluid flow line segment. For example, as shown in FIGS.7A and 8, each segment a, b, c of each fluid flow line 160, 162, 164 canhave multiple corrugated and non-corrugated portions 170, 172. Thecorrugated portions 170 correspond to the locations where the variousfluid flow lines are bent, such as at the end of the middle segmentwhere the fluid lines flare away from each other to pass through endplate 148 of common-access tube 28. Additionally, the opposite ends ofthe middle segments can also have corrugated portions that facilitatethe upward bending of these fluid flow lines in the space between theinner and outer vessels 22, 24. Furthermore, if desired, the interiorsegments 160 a, 162 a, 164 a of these various fluid flow lines can alsohave corrugated portions 170 and non-corrugated portions 172 thatcorrespond to the various portions of the fluid flow lines that are bentor remain straight.

The use of non-corrugated portions 172 in each of the fluid flow linesegments provides a level of stiffness or rigidity that is not availablewhen only, corrugated portions are used. These non-corrugated portions172 thereby help to stiffen the fluid-flow line segments and maintainthe fluid flow line segments in their desired orientation duringoperation of storage tank 20. The non-corrugated portions 172 alsominimize and/or eliminate the need for additional bracing or framing toretain the fluid flow lines in their desired orientation duringoperation of storage tank 20. Additionally, by limiting the use ofcorrugated portions 170 to those areas that are required to be bent, thepotential for elongation of the various fluid flow lines due to pressuredifferentials during the operation of storage tank 20 is reduced. Thus,the use of fluid flow line segments having both corrugated andnon-corrugated portions is advantageous over the use of an entirelycorrugated segment.

The use of corrugated and non-corrugated portions 170, 172 for thevarious segments of the fluid flow lines 26 also facilitates theassembly of storage tank 20 and, particularly, facilitates theconstruction of modular assemblies that can be used to form storage tank20. The various fluid flow lines 26 can be formed in straight and unbentsegments with corrugated and non-corrugated portions 170, 172 dispersedthroughout its length. These various segments can then be attached toone or more components, such as common-access tube 28 at end plates 148,150 therein, or other fluid flow line segments to form a modularassembly. The modular assemblies can then be inserted into or attachedto other components of storage tank 20 in a piecemeal fashion to formstorage tank 20, as described below.

Referring now to the flow charts of FIGS. 14-17, the method ofassembling storage tank 20 is shown. Storage tank 20 is formed byassembling inner vessel 22 and fluid flow lines 26 that extend intointerior 46 of inner vessel 22, as indicated in block 190. Theassembling of inner vessel 22 is shown in FIG. 15. To assemble innervessel 22, a modular assembly of common-access tube 28, fluid flow lines26, sensor(s) and, optionally, end cap 42 is formed, as indicated inblock 192. There are two main ways to form this modular assembly, asshown in, blocks 194 and 196. Either method shown in block 194 or 196can be utilized.

The methods shown in block 194 are discussed first. In this method ofpreparing the modular assembly, the fluid flow lines 26 are firstattached to end plate 148, as indicated in block 194 a. To accomplishthis, a portion of each fluid flow line 26 is inserted through one ofthe openings in end plate 148 so that it protrudes out the oppositeside. The fluid flow line is welded with welds W, as shown in FIG. 7B,to end plate 148 to form a fluid-tight seal therebetween. The fluid flowlines 26 can each be individually inserted through its associatedopening and welded in place with welds W or, alternatively, all thefluid flow lines can be inserted and then subsequently welded with weldsW one at a time. The spacing between the fluid flow lines 26 on endplate 148, as shown in FIG. 7B, prevents the fluid flow lines frominterfering with each other during the welding process. If the fluidflow lines have not been pre-bent into a desired orientation, the fluidflow lines can then be bent into the proper orientation for subsequentrunning of the fluid flow lines through common-access tube 28. Toaccomplish this, the corrugated portions 170 of the fluid flow lines canbe bent so that the fluid flow lines will match the flared portion 146and uniform diameter portion 144 of common-access tube 28. With thefluid flow lines attached to end plate 148 and arranged into the desiredorientation, the fluid flow lines are inserted through common-accesstube 28 from the second end 142, as indicated in block 194 b. The freeends of fluid flow lines 26 are inserted through the opening(s) in endplate 150 on first end 140 of common-access tube 28, if so equipped. Endplate 148 is aligned with second end 142 and attached to common-accesstube 28 by welding, as shown in FIG. 7B and as indicated in block 194 c.Optionally, the fluid flow lines 26 can also be secured to end plate150, if so equipped. Thus, one way to attach fluid flow lines 26 tocommon-access tube 28 can be done by following the procedures indicatedin block 194.

Alternately, the fluid flow lines 26 can be attached to common-accesstube 28 by following the procedures shown in block 196. To start, endplate 148 is aligned with second end 142 of common-access tube 28 andattached thereto, such as by welding, as shown in FIG. 7B and asindicated in block 196 a. Next, fluid flow lines 26 are inserted intocommon-access tube 28 and through the openings in end plate 148, asindicated in block 196 b. Depending upon the construction, theprocedures in blocks 196 b and 196 a may be reversed. For example, ifcommon-access tube 28 has a flared portion 146, fluid flow lines 26 arefirst bent into a desired configuration and inserted into common-accesstube 28 and end plate 148 is then slid over fluid flow lines 26 andwelded to second end 142 of common-access tube 28. Each fluid flow line26 can then be welded to end plate 148, as shown in FIG. 7B and asindicated in block 196 c. If, however, the common-access tube has auniform diameter throughout, fluid flow lines 26 can be inserted throughcommon-access tube 28 and through the openings in end plate 148 (alreadywelded to the common-access tube) and then welded thereto, as shown inFIG. 7B and as indicated in block 196 c. End plate 150, if desired, canthen be positioned in the first end 140 of common-access tube 28 andattached thereto. The fluid flow lines 26 can also be secured to endplate 150. Thus, by following the procedures in block 196, a second wayof assembling common-access tube 28 with fluid flow lines 26 can beachieved.

Regardless of the manner in which fluid flow lines 26 are attached tocommon-access tube 28, the modular assembly is continued to be assembledby attaching sensor(s), such as level sensor 152, to the exterior ofcommon-access tube 28, as indicated in block 198. Once all these sensorsare attached to common-access tube 28, the common-access tube isattached to end cap 42 of inner vessel 22, as indicated in block 200. Toaccomplish this, first end 140 of common-access tube 28 is aligned witha central axial opening in end cap 42 with portions of fluid flow lines26 extending through the opening in end cap 42 and through bracket 48(if already attached). First end 140 is then welded to end cap 42 withcommon-access tube 28 at a desired angle relative to the axial axis ofinner vessel 22. Preferably, fluid flow lines 26 extend a substantialdistance beyond end cap 42 and past bracket 48 thereon, as shown in FIG.7A. Next, the interior segments 160 a, 162 a, 164 a are attached to themiddle segments 160 b, 162 b, 164 b of fluid flow lines 26, as indicatedin block 202 by welds W. The interior segments can be provided aspre-bent segments or as straight segments including both corrugated andnon-corrugated portions. With the former, the appropriate end of eachinterior segment is aligned with the associated middle segmentpositioned in desired orientation, and welded thereto. This is repeatedfor each of the interior segments. With the latter construction, theappropriate end of each interior segment is aligned with the associatedmiddle segment and welded thereto. Once the interior segments areattached to the middle segments, each interior segment can then be bentinto the desired configuration by bending the corrugated portions ofeach interior segment, as indicated in block 204.

With the interior and middle segments of each fluid flow line secured tocommon-access tube 28, the communication or signal lines for the varioussensors that are to be disposed within interior 46 of inner vessel 22can be routed through one of the fluid flow lines. It should, beappreciated that the manufacturing steps performed in blocks 200 and 202can be reversed in sequence, depending upon the desired order ofconstruction. Regardless of the sequence in which the manufacturing ofthe modular assembly is conducted, a modular assembly that includes boththe interior and middle segments of fluid flow lines 26, common-accesstube 28, the internal sensors and end cap 42 are assembled together intoa modular assembly and can be used to form inner vessel 22.Specifically, the modular assembly is aligned with central segment 40 ofinner vessel 22 and then attached thereto, such as by welding, asindicated in block 206. Alignment of the modular assembly with centralsegment 40 can be performed by the use of jigs or other suspensionmechanisms (not shown) to support and position the modular assembly inalignment with central segment 40 so that the welding of end cap 42 tocentral segment 40 is facilitated. If not already done, end cap 44 isaligned with central segment 40 and attached thereto, such as bywelding, as indicated in block 208. With these procedures complete, theassembly of inner vessel 22 is completed.

Referring back to FIG. 14, once inner vessel 22 is assembled, the nextstep in preparing storage tank 20 is the application of insulationlayers 30 to inner vessel 22, as indicated in block 210. To accomplishthis, inner vessel 22 can be positioned on a jig or other supportstructure (not shown). The insulation layers 30 are then wrapped,preferably in a tangential direction, around central segment 40 and endcaps 42, 44. The application of the insulation layers can be manual orautomated. The insulation layers are folded over end caps 42, 44 andaround the obstructions formed by bracket 48 and tensioning mechanism50. With all of the fluid flow, lines 26 and signal lines for thevarious sensors within inner vessel 22 exiting inner vessel 22 throughcommon-access tube 28, the number of obstructions to accommodate arereduced and automated application of insulation layers 30 isfacilitated. Once the insulation has been applied to inner vessel 22,the next stage in the assembly of storage tank 20 is the suspending ofinner vessel 22 within central segment 60 of outer vessel 24, asindicated in block 212.

Referring to FIG. 16, a procedure to suspend inner vessel 22 withincentral segment 60 of outer vessel 24 is shown. Inner vessel 22 ispositioned within central segment 60 of outer vessel 24, as indicated inblock 214. A jig or other support structure (not shown) can be used tosupport inner vessel 22 when it is within central segment 60 prior tobeing suspended by suspension members 80. With inner vessel 22 inposition, first group 82 of suspension members 80 are attached torollers 88 coupled to an associated stiffening member 68 and to rollers94 on bracket 48 on end cap 42, as indicated in block 216. To accomplishthis, each roller 88 is inserted into the loop formed by a suspensionmember 80 and attached to its associated bracket 90 on stiffening member68. Similarly, each roller 94 is also inserted into an associated loopof a suspension member 80 and then attached to its associated bracket 48on end cap 42 of inner vessel 22. The fixed length of the suspensionmember loops secure end 42 of inner vessel 22 within one end portion 70of central segment 60.

Next, second group 84 of suspension members 80 are attached to therollers 88 coupled to the associated stiffening member 68 and to also torollers 100 on tensioning mechanism 50, as indicated in block 218.Again, this is accomplished by disposing each roller 88 within one ofthe suspension member loops 80 and attaching it to its associatedbracket 90 on stiffening member 68. Similarly, each roller 100 is alsodisposed within one of the suspension member loops 80 and attached tobracket member 115. The fixed length of each suspension member loop 80allows end 44 of inner vessel 22 to be suspended within the other endportion 70 of central segment 60 of outer vessel 24. The jig ormechanism holding inner vessel 22 within outer vessel 24 can then beremoved and inner vessel 22 suspended within central segment 60 by firstand second groups 82, 84 of suspension members 80. It should beappreciated that the procedures indicated in blocks 216 and 218 can bedone in the opposite order, if desired.

With inner vessel 22 suspended within outer vessel 24 by suspensionmembers 80, tensioning mechanism 50 is then adjusted to apply a desiredpreloading or predetermined tension in suspension members 80, asindicated in block 220. To accomplish this, adjusting member 116 isrotated to cause movable plate 112 to move relative to base plate 110.Movement of movable plate 112 relative to base plate 110 should causethe tension in each suspension member of both first and second groups82, 84 to change. That is, because the suspension members extend bothaxially and radially relative to their associated connection to the ends42, 44 of inner vessel 22, each suspension member imparts an axial andradial suspending force on the associated end of inner vessel 22. Thus,when tensioning mechanism 50 is adjusted, the level of tension in eachsuspension member 80 should change. The radial suspension forces ofsuspension members 80 constrain the movement of inner vessel 22 withinouter vessel 24 in two directions, while the axial suspending forceallows for limited movement in a third (axial) direction. Thus, innervessel 22 is suspended within central segment 60 of outer vessel 24 withstiffening members 68 supporting end portions 70 of central segment 60and limiting the deformation thereof due to the suspension of innervessel 22 therein.

Referring back to FIG. 14, another stage of manufacturing storage tanks20 is the assembly of outer vessel 24, as indicated in block 224. Theassembly procedure of outer vessel 24 is shown in FIG. 17. Once innervessel 22 is suspended within central segment 60, the exterior segmentsof fluid flow lines 26 can be attached to the portion of the middlesegments that extend out of common-access tube 28 with welds W, asindicated in block 230. Preferably, the middle segments extend beyondinner vessel 22 a distance sufficient to allow the welding of theexterior segments onto the middle segments without damaging orendangering insulation layers 30. Once each exterior segment is weldedto its associated middle segment, the portion of the middle segmentextending out of common-access tube 28 and the exterior segmentsattached thereto can be bent into a predetermined orientation, asindicated in block 232. The bending is facilitated by the existence of avariety of corrugated portions 170 and non-corrugated portions 172 ineach of the segments of the fluid flow lines. For example, as shown inFIGS. 8 and 9, the middle segments 160 b, 162 b, 164 b would extendoutwardly beyond the common-access tube 28 and can be bent upwardly toprovide a desired rise in elevation of these associated fluid flow lines26. The exterior segments 160 c, 162 c, 164 c could also be bent attheir various corrugated portions 170 to provide a desired orientation,such as that shown in FIGS. 8 and 9.

The exterior segments 160 c, 162 c, 164 c are routed to communicate withthe exterior of outer vessel 24 by one of two ways, as indicated inblocks 234 and 236. One method is to attach exterior segments 160 c, 162c, 164 c to associated piping (not shown) that extends into the interiorof central segment 60 of outer vessel 24, as indicated in block 234. Thepiping can extend beyond end portion 70 so that the exterior segments ofeach fluid flow line 26 can be easily welded thereto withoutjeopardizing the integrity of insulation layers 36. Alternately, asindicated in block 236, the exterior segments 160 c, 162 c, 164 c can berouted through openings (not shown) in central segment 60 of outervessel 24 and subsequently attached thereto, such as by welding. Ifdesired, the various fluid flow lines can be mixed or matched betweenthe two possibilities disclosed in blocks 234 and 236. Due to the use ofnon-corrugated portions 172 between corrugated portions, 170, thestiffness of exterior segments 160 c, 162 c, 164 c should be sufficientto provide support for the fluid flow lines without requiring additionalsupport or connection points/brackets.

Regardless of how the exterior segments 160 c, 162 c, 164 c are secured,the next step is to attach end caps 62, 64 to outer vessel 24, asindicated in block 238. To accomplish this, end caps 62, 64 are placedin alignment with end portions 70 of central segment 60. Portions ofstiffening members 68 extend beyond end portions 70 and will extend intoend-caps 62, 64, as shown in FIGS. 1 and 4. End caps 62, 64 are thenwelded to central segment 60 with weld W. The overlapping of stiffeningmembers 68 across the juncture of end portions 70 of central segment 60with end caps 62, 64 inhibits the entry of sparks and other debris fromthe welding process into the space between inner and outer vessels 22,24 and onto the insulation layers 30 therein.

With outer vessel 24 assembled, a vacuum is formed between inner andouter vessels 22 and 24, as indicated in block 240. The assembly ofcryogenic storage tank 20 is now complete. The attachment of end caps62, 64 to central segment 60 provides further support for centralsegment 60 against the load imparted by the suspension of inner vessel22 therein. Due to the support of stiffening members 68 on centralsegment 60, the alignment of end caps 62, 64 with central segment 60 isfacilitated because of the limited deformation of end portions 70 as aresult of suspending inner vessel 22 therein.

While the present invention has been described with reference tospecific configurations and procedures for forming the cryogenic storagetank, it should be appreciated that variations can be employed withoutdeparting from this spirit and scope of the present invention. Forexample, each fluid flow line could include discrete segments havingboth corrugated and non-corrugated portions and discrete segments thatare free of corrugated portions. Additionally, the various segments may,include pre-bent segments and segments having corrugated andnon-corrugated portions. Additionally, some segments could be pre-bentin some areas and have corrugated portions for subsequent bending duringthe assembly of storage tank 20. Moreover, the length of the varioussegments can vary and, in some cases, one or more of the fluid flowlines can be a single unitary uninterrupted flow line. Additionally, theorientation of the fluid flow lines 26 is shown for one particularconstruction of a storage tank 20. It should be appreciated that otherfinal orientations for the fluid flow lines 26 can be employed, asnecessitated by the design of storage tank 20, without departing fromthe scope of the present invention. Moreover, it should be appreciatedthat common-access tube 28 could extend through a non-axial centeredportion of an end-cap of inner vessel 22, if desired, although all thebenefits of the present invention may not be realized. Additionally,while the modular assembly is discussed as including specificcomponents, it should be appreciated that additional components or lesscomponents can be assembled into a modular pre-assembly and then used toform various portions of storage tank 20. As such, the construction ofthe present invention facilitates the preparation of various modularcomponents that can be made in one location and, if desired, moved to asecond location for assembly into the remaining components to formstorage tank 20. Thus, the above description of the invention is merelyexemplary in nature, and variations that do not depart from the gist ofthe invention are intended to within the scope of the invention. Assuch, such variations are not to be regarded as a departure from thespirit and scope of the invention.

1. A cryogenic storage tank comprising: a fluid-tight outer vessel; afluid-tight inner vessel disposed within the outer vessel; a vacuumbetween the inner and outer vessels; a tube communicating with thevacuum and extending into an interior of the inner vessel, a firstportion of the tube within the interior of the inner vessel having afirst cross-sectional area of a first value, a second portion of thetube within the interior of the inner vessel having a secondcross-sectional area of a second value greater than the first value, thesecond portion being an end portion; and a plurality of fluid linesextending from an exterior of the inner vessel to an interior of theinner vessel through the tube.
 2. The storage tank of claim 1, whereinthe second portion of the tube is a flared end portion.
 3. The storagetank of claim 2, wherein the fluid lines pass through an end plate inthe flared end portion of the tube.
 4. The storage tank of claim 3,wherein the first portion of the tube is a straight portion.
 5. Thestorage tank of claim 3, wherein the first and second portions areaxially aligned.
 6. The storage tank of claim 3, wherein the firstportion of the tube extends from an axial center portion of an end ofthe inner vessel.
 7. A modular component for a cryogenic storage tank,the modular component comprising: a tube having first and second ends;an end plate on the second end of the tube; and a plurality of fluidflow lines extending through the tube and through the end plate with afluid-tight connection between an exterior of the fluid supply lines andthe end plate, wherein the tube, end plate and fluid flow lines areconnected together as a single assembly operable to be attached to aninner vessel of a cryogenic storage tank prior to the inner vessel beingenclosed within an outer vessel of the cryogenic storage tank.
 8. Themodular component of claim 7, further comprising a liquid level sensorattached to an exterior of the tube and forming part of the assembly. 9.The modular component of claim 8, further comprising a signal lineattached to the sensor and routed through one of the fluid flow lines.10. The modular component of claim 7, wherein the plurality of fluidflow lines include stubs projecting outwardly from the end plate andfurther comprising internal fluid flow lines connected to the stubs andwhich reside within the interior of the inner vessel when assembledwithin the outer vessel of the cryogenic storage tank.
 11. The modularcomponent of claim 7, further comprising an inner vessel end capconnected to the tube and forming part of the assembly and operable tobe connected to a central segment of the inner vessel.
 12. A method ofassembling a cryogenic storage tank having a fluid-tight inner vessellocated within a fluid-tight outer vessel and a plurality of fluid flowlines extending from an exterior of the outer vessel to an interior ofthe inner vessel through a common-access tube, the method comprising:(a) attaching a plurality of fluid flow lines to an end plate with firstportions of the fluid flow lines extending beyond a first side of theend plate and second portions of the fluid flow lines extending beyond asecond side of the end plate, the end plate configured to be disposed inthe common-access tube with the first side of the end plate exposed tothe interior of the inner vessel and the second portions of the fluidflow lines within the common-access tube; and (b) attaching interiorfluid piping members to the first portions of the fluid flow lines. 13.The method of claim 12, further comprising welding the end plate to afirst end portion of the common-access tube prior to performing (a). 14.The method of claim 13, wherein (a) includes inserting the fluid flowlines through an entire length of the common-access tube and through theend plate prior to attaching the fluid flow lines to the end plate. 15.The method of claim 14, wherein (a) includes inserting the fluid flowlines through the end plate from the second side of the end plate. 16.The method of claim 13, further comprising welding the end plate to aflared end portion of the common-access tube prior to performing (a).17. The method of claim 12, wherein (a) includes attaching the pluralityof fluid flow lines to the end plate with the fluid flow lines uniformlyspaced apart at the end plate.
 18. The method of claim 12, wherein (a)includes welding the fluid flow lines to the end plate.
 19. The methodof claim 12, further comprising welding the end plate to a first endportion of the common-access tube after performing (a).
 20. The methodof claim 12, wherein (a) includes inserting all of the fluid flow linesthrough openings in the end plate prior to attaching each of the fluidflow lines to the end plate.
 21. The method of claim 12, furthercomprising bending the interior fluid piping members into apredetermined configuration.
 22. The method of claim 12, furthercomprising attaching a liquid level sensor to an exterior portion of thecommon-access tube.